Add unlifting pass under private config (#104897)
Summary: We wanna do this little by little. For now, I tried only on DissectedPartsModel which needs to use aot_export version.
Test Plan: CI
Reviewed By: zhxchen17
Differential Revision: D46785735
Pull Request resolved: https://github.com/pytorch/pytorch/pull/104897
Approved by: https://github.com/JacobSzwejbka
